Antifoggants and stabilizers for photographic silver halide emulsions



tates 3,023,103 ANTHOGGANTS AND STABILIZERS FOR PHOTO- GRAPHIC SILVER HALIDE EMULSIONS Fritz Dersch and Millet R. De Angelus, Binghamtou,

N.Y., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 2, 1960, Ser. No. 46,906

7 Claims. (Cl. 96109) the silver halide emulsion. Although many of these com-.

pounds have the ability to reduce the fog tendencies and to improve the stability of the emulsion, they are deficient in that they lower the sensitivity of the emulsions and often reduce optical and dye sensitivity.

We have now discovered that heterocyclic compounds containing a simple-S-membered nitrogenous heterocyclic ring, the 2-position of which is substituted with a guanidino radical, are not only excellent stabilizers or antiiogging agents for light-sensitive silver halide emulsions but, in addition, have the faculty of performing this function without lowering the sensitivity of the emulsion with which they are associated or without reducing the sensitivity of the emulsion to light of longer Wave length attributable to the presence of sensitizing dyes.

The use of such compounds to inhibit fog and to stabilize silver halide emulsions either by locating the same in the emulsion or in layers adjacent thereto or in processing baths for the emulsion constitutes the purposes and objects of the present invention.

The an-tifoggants the use of which are contemplated herein may be represented by the following formula:

NHa

wherein X represents the radicals necessary to form a benzo ring and Y is S, O or NH.

Examples of compounds Within the ambit of such formula which we have found to be effective are:

Z-guanidino-benzimidazole of the following formula- S-chloro-2-guanidino-benzimidazole 4,6-dichloro-2-guanidino-benzimidazole 5 ,6-dichloro-Z-guanidino-benzimidazole 4,5,6-trichloro-2-guanidino-benzimidazole 5-bromo-Z-guanidino-benzimidazole 3,023,103 Patented Feb. 27, 1962 ice S-nitro-2-guanidino benzimidazole 5-methoxy-2-guanidino-benzimidazole 5-methyl-2-guanidino-benzimidazole 4,6-dimethyl-2-guanidino-benzimidazole S-phenyl-Z-guanidino-benzimidazole 4,6-dinitro-2-guanidino-benzimidazole and the like 2-guanidino-benzthiazole of the following formula and such compounds substituted in the 5-position by chloro, bromo, nitro, methoxy or methyl or in the 4,6- and 5,6-position by chloro or bromo Z-guanidino-benzoxazole of the following formula and such compounds substituted in the 5-position by chloro, bromo, nitro, methoxy, methyl, phenyl or in the 4- and 6- or 5- and 6-positions by chloro or bromo,

and in the 4- and 6-positions by methyl.

The products utilizable herein are prepared by reac-- tion of orthophenylenediamine-dicyandiamide with an orthophenylene-diamine (benzimidazole), with an orthoaminobenzenethiol (benzthiazole) or with an ortho-aminc-phenol (benzoxazole). The reactions are conventional and are described in the literature.

The invention will be further illustrated by the following examples in which the parts are by weight.

Example I 1 kilogram of a silver halide emulsion ingelatin containing 2% of silver iodide and 98% of silver bromide Was prepared in a conventional manner. A 1% solution of Z-guanidino-benzimidazole was added to the emulsion as an antifoggant and stabilizer. The emulsion samples contained 0.6 mol of silver halide. The emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type IIB Sensitometer in a developer of the follow ing composition:

3 I The Z-guanidino-benzimidazole was prepared as folows:

10 grams of orthophenylenediam-ine-dihydrochloride were dissolved in 100 milliliters of water. To .the solution were added 10 grams of dicyandiamide and the reaction mixture heated to reflux for 5 hours. The reaction mixture was allowed to cool at room temperature and 20 milliliters of a 40% sodium hydroxide solution were added. Yellowish plate-like crystals precipitated and were chilled and collected. The solid was recrystallized from boiling water after previous charcoal treatment. The product-the pure monohydrate-rnelted at 237- 238 C.

Example [I The procedure was the same as in Example I with the exception that the guanidino-benzimidazole was replaced by the same amount of 2-guanidino-benzthiazole.

The results were similar to those obtained in Example I.

The Z-guanidino-benzthiazole was prepared by dissolving 12.5 grams of ortho-aminobenzenethiol in 100 milliliters of ethanol and 40 milliliters of concentrated hydrochloric acid. 8.4 grams of dicyandiamide were added and the reaction mixture refluxed for 3 hours. The preparation was chilled in an ice bath and a white solid precipitated. The solid was collected and washed with cold water. Conversion to the free base was effected by dissolving the hydrochloride obtained above in 200 milliliters of hot water and 30 milliliters of a 40% solution of sodium hydroxide. The free base separated immediately and was collected and crystallized twice from an ethanol-water mixture after previous charcoal treatment. The product was pearly white and melted at 167-8 C.

Example III The procedure was the same as in Example I excepting that the guanidino-benzimidazole was replaced by the same amount of Z-guanidino-benzoxazole.

The results were similar to those obtained in Example I.

The Z-guanidino-benzoxazole was prepared by dissolving 100 grams of ortho-arninophenol in a mixture of 100 milliliters of concentrated hydrochloric acid and 100 milliliters of ethanol. After heating to reflux for 15 minutes, 80 grams of dicyandiamide were added and the heating continued for 2.5 hours. The reaction mixture was chilled and filtered to yield a dark brown solid weighing 130 grams. Conversion to the free base was effected by dissolving 50 grams of hydrochloride in 300 milliliters of boiling water. To this were added 13 grams of potassium hydroxide in S milliliters of water. The base separated immediately and after cooling was filtered and washed with cool water. The product was crystallized by dissolving in ethanol and treating with charcoal. It was poured into a large volume of water and a second crystallization was efiected by dissolving in boiling water. The pale yellow plates obtained melted at 183-4" C.

Example IV Example V- The procedure was the same as in Example IV excepting that the 2-guanidino-benzimidazole was replaced by S-chloro-Z-guanidino-benzimidazole..

The results were similar to those of ExampleIVs The 5-chloro-Z-guahidino-benzimidazole was prepared in the same way as the Z-guanidino-benzimidazole except 4. ing that in lieu of orthophenylenediamine-dihydrochloridc there was employed 4-chloro-orthophenylenediamine-dihydrochloride.

Any of the above-noted guanidino compounds may be used in lieu of those of the examples. They may be prepared by using in lieu of the orthophenylenediamine-dihydrochloride, orthoaminobenzenethiol or ortho-aminophe- 1101, the correspondingly substituted, disubstituted or trisubstituted parent material. For example, 4,6-dichloro-2- guanidino-benzimidazole was prepared while using 3,5-dichloro-orthophenylenediamine, S-nitro-Z-guanidino-benzthiazole was prepared while starting with 4-nitro-orthoaminobenzenethiol in lieu of the ortho-amino-benzenethiol. Similarly, 4,6-dimethyl-2-guanidino-benzoxazole was prepared by starting with 3,S-dirnethyl-ortho-aminophenol rather than the ortho-arninophenol.

Beneficial effects and fog reduction are obtained when solutions of the aforementioned compounds are incorporated in the silver halide emulsions as ripening finals or as coating finals. Ripening finals are added during the ripening or the sensitivity increasing stage of the emulsion making process. Such additions may be made before, during or after the decomposition of the soluble silver salt such as silver nitrate by means of soluble halides such as potassium bromide in the presence of a colloidal carrier such as gelatin, PVA, solubilized casein or albu- Coating finals are added to the emulsion just prior to coating on a suitable support such as glass, paper or film at a time when the emulsion has nearly obtained its maximum sensitivity.

When used as ripening finals, the antifoggants or stabilizers hereof are best used in a concentration of l to 25 milligrams per 0.6 mol of silver halide and when used as coating finals in a concentration of 10 to 300 milligrams per 0.6 mol of silver halide. The concentration used depends on the type of emulsion employed, and it is advisable to determine the optimum concentration from case to case. In some instances, it is advantageous to apply the antifoggant in an adjacent layer, i.e., in a separate undercoating layer or in an anti-abrasion gelatin overcoating. In other cases, desirable results accrue when they are employed in the processing baths.

The antifoggants which we utilize may be employed in various types of photographic emulsions, e.g., non-sensitized, orthochromatic, panchromatic, X-ray emulsions and color emulsions. They may be used in combination with other antifoggants and stabilizers or in combination with sulfur, reductionand metal-sensitizers or with polyoxyethylene accelerators.

Various modifications of the invention will occur to persons skilled in the art. Thus, it is evident that in lieu of the examples any of the antifoggants specifically mentioned may be employed. We, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. Light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion thereon, said light-sensitive material containing as an antifoggant a compound of the following constitution:

NH x C-NHO NH; N

wherein X represents the atoms necessary to form a benzo radical and Y is selected from the class consisting of S, O and NH.

2. The article as defined in claim 1 wherein said antifoggant is located in the silver halide emulsion.

3. The article as defined in claim 1 wherein the antifoggant is located in a layer adjacent to the silver halide emulsion.

4. Light-sensitive photographic material comprising a base with a light-sensitive silver halide emulsion thereon, said emulsion containing as an antifoggant the compound Z-guanidino-benzimidazole.

5. Light-sensitive photographic material comprising a base with a light-sensitive silver halide emulsion thereon, said emulsion containing as an antifoggant the compound Z-guanidino-benzoxazole.

6. Lightensitive photographic material comprising a base with a light-sensitive silver halide emulsion thereon, said emulsion containing as an antifoggant the compound Z-guanidino-benzthiazole.

7. The process of minimizing and preventing fog in light-sensitive silver halide materials comprising a base in which X represents the atoms necessary to form a benzo ring and X is selected from the class consisting of O, S and NH.

No references cited. 

7. THE PROCESS OF MINIMIZING AND PREVENTING FOG IN LIGHT-SENSITIVE SILVER HALIDE MATERIALS COMPRISING A BASE HAVING A LIGHT-SENSITIVE SILVER HALIDE EMULSION THEREON, WHICH COMPRISES EXPOSING THE EMULSION AND DEVELOPING THE SAME IN THE PRESENCE OF AN ANTIFOGGANT OF THE FOLLOWING FORMULA: 